The way the stars in Galaxy are weighted relies heavily on the weak equivalence principle (Third Kepler Law). This law was verified in Solar System for baryonic matter – the planets and satellites rotating around the Sun. No deviations from this law was found (assuming the GR corrections). However, the Sun has a lot of non-baryonic matter inside (the photons are trapped inside for millions of years, slowly progressing toward the surface). The gravitation properties of such non-baryonic matter were never carefully investigated: unfortunately the Sun is not a binary star and gravitational attraction of two stars in the solar system was never checked. Observations of visual binaries may help to check the validity of the third Kepler law for stars motion. Re-analysis of the old data (1972) on binaries gives a hint that the slope of the mass-luminosity relation (the best way to measure the distant star) depends upon the choice of stars. This unusual observation may hint onto the violation of third Kepler Law for stars dynamic. If confirmed on large databases, this observation may resolve the dark matter problems: the stars are heavier than expected and gravitationally much heavier than expected and it may lead to re-evaluation of the mass of galaxies and as a consequence to elimination of the dark matter hypothesis for galaxies rotation.